Construction cable

ABSTRACT

The cable, in particular of the stay cable type, comprises a set of traction reinforcements, two devices for anchoring the reinforcements in two respective zones of the construction, the reinforcements being spaced apart from one another at the anchoring devices, means for deviating the reinforcements in order to cause the reinforcements to converge toward a running part of the cable into a substantially parallel bundle which is more compact than at the anchoring devices, and a guide member which is in closely set contact around the set of reinforcements. This member has an inner surface, the cross section of which is adapted to the peripheral shape of the parallel bundle and the longitudinal section of which has a convex curvature which, over the length of the guide member, allows angular deflections of the reinforcements which are substantially greater than the maximum angle of convergence of the reinforcements between the anchoring device and the running part of the cable.

The present invention relates to the field of cables used in buildingfor participating in the structure of certain civil engineeringconstructions.

It is aimed more particularly at arrangements of such cables which givethem good properties in the event of an earthquake.

The invention is especially applicable to the stay cables used forsuspending portions of the construction, such as bridge decks. In acurrent embodiment, such a stay cable comprises a bundle of parallelreinforcements extending between two anchoring zones, one arranged on apylon of the construction and the other on the suspended part. In theanchoring zone, the individual reinforcements of the stay cable have aslight divergence, so that they can be locked individually.

When a stayed construction experiences an earthquake, the suspendedpart, for example the bridge deck, undergoes abrupt and potentiallyconsiderable displacements with respect to the pylons. This results inhigh variations in traction and in flexion in the stay cables.

The flexural stresses are reflected in the anchoring zones and riskdamaging the reinforcements and/or the anchoring devices.

The document WO 00/75453 describes an anchoring device for a structurecable, such as a stay cable, provided with guide means comprising anindividual guide duct for each reinforcement, this duct widening in thedirection of the running part of the cable, so as to allow an angulardeviation of the reinforcement. The advantage of this anchoring deviceis that it ensures a progressive take-up of the flexural forcesattributable to the convergence of the reinforcements toward the runningpart or of some transverse actions experienced by the stay cable.However, this force take-up may prove insufficient in the presence ofthe violent stress variations undergone in the event of an earthquake.

An object of the present invention is to propose an arrangement makingit possible for the structure cables and for the constructions of whichthey form part to withstand the high stresses occurring in the event ofan earthquake.

The invention thus proposes a civil engineering structure cable,comprising:

-   -   a set of traction reinforcements;    -   two devices for anchoring the reinforcements in two respective        zones of the construction, the reinforcements being spaced apart        from one another at the anchoring devices; and    -   means for deviating the reinforcements to cause the        reinforcements to converge toward a running part of the cable        into a substantially parallel bundle which is more compact than        at the anchoring devices.

According to the invention, the structure cable comprises at least oneguide member which is in closely set contact around the set ofreinforcements and which has an inner surface, the cross section ofwhich is adapted to the peripheral shape of the parallel bundle and thelongitudinal section of which has a convex curvature which, over thelength of the guide member, allows angular deflections of thereinforcements which are substantially greater than the maximum angle ofconvergence of the reinforcements between the anchoring device and therunning part of the cable.

The form of the guide member allows it absorb high angular deflectionsof the set of reinforcements, with a controlled radius of curvature inorder to avoid damaging the reinforcements and the anchoring device.

In preferred embodiments of the cable according to the invention:

-   -   the angular deflections allowed by the guide member are of at        least 100 milliradians;    -   the angular deflections allowed by the guide member are at least        double the maximum angle of convergence of the reinforcements        between the anchoring device and the running part of the cable;    -   the radius of curvature of the longitudinal section of the inner        surface of the guide member is at least 3 meters in the portion        where this member is in closely set contact around the set of        reinforcements;    -   the radius of curvature of the longitudinal section of the inner        surface of the guide member decreases from the portion where the        member is in closely set contact around the set of        reinforcements toward the running part of the cable;    -   the guide member is mounted with a capacity for transverse        movement with respect to one of the anchoring devices;    -   means for the damping of transverse vibrations of the bundle of        reinforcements with respect to one of the anchoring devices are        provided, and the guide member is placed on the set of        reinforcements between the damping means and said anchoring        device;    -   the guide member is mounted with a limited capacity for        transverse movement with respect to said anchoring device, so as        to provide a defined stroke of the damping means;    -   the anchoring device bears longitudinally against a tube which        is connected to the structure of a part of the construction and        through which the reinforcements pass, the damping means        comprise a damper arranged between the bundle of reinforcements        and a support mounted at that end of said tube which is opposite        the anchoring device, and the mounting of the support at the end        of the tube is carried out by means of a connection designed to        break when it is subjected to a force exceeding a predefined        threshold;    -   the deviation means comprise a collar clamped around the set of        reinforcements at a distance from an anchoring device, and the        guide member is placed on the set of reinforcements between said        collar and said anchoring device;    -   inserts are seated, together with the reinforcements, in the        guide member, so as to maintain a spacing between the        reinforcements inside the guide member;    -   said inserts comprise plastic sleeves placed individually around        the reinforcements inside the guide member, the inner surface of        the guide member preferably having a hexagonal cross section;    -   the guide member belongs to the deviation means, at the same        time contributing to causing the reinforcements to converge        toward the running part of the cable;    -   the guide member comprises a body of cast plastic resin around a        metal reinforcing tube, and this plastic resin may, in        particular, be a polyurethane resin.

Another aspect of the present invention relates to a guide member for astructure cable, as defined above. This member has a tubular generalshape, with an inner surface to be applied in closely set contact arounda set of traction reinforcements, the set of reinforcements convergingbetween an anchoring device and a running part of the cable where thereinforcements are gathered into a parallel bundle which is more compactthan at the anchoring device, said inner surface having a cross sectionadapted to the peripheral shape of said bundle and a longitudinalsection having a convex curvature which, over the length of the guidemember, allows angular deflections of the reinforcements which aresubstantially greater than the maximum angle of convergence of thereinforcements between the anchoring device and the running part of thecable. Said inner surface preferably has a hexagonal or circular crosssection.

Other particular features and advantages of the present invention willbecome apparent from the following description of a nonlimitingexemplary embodiment, with reference to the accompanying drawings inwhich:

FIG. 1 is a diagrammatic side view of a cable stayed bridge to which theinvention may be applied;

FIG. 2 is a diagrammatic view, in longitudinal section, of a part of astay cable according to the invention; and

FIGS. 3 to 5 are cross-sectional views of this stay cable, takenrespectively along the planes III-III, IV-IV and V-V indicated in FIG.2.

The invention is described below, without this being limiting, withregard to a structure cable consisting of a bridge stay cable.

A cable stayed bridge is illustrated diagrammatically in FIG. 1. Thedeck 1 of the bridge is supported by sets of stay cables 2 with one ormore pylons 3 erected in the zone through which the bridge passes. Eachstay cable 2 follows a defined path between a bottom anchoring device 4mounted on the deck 1 and a top anchoring device 5 mounted on the pylon3.

FIG. 2 shows in more detail the structure of the stay cable in the deckzone where the anchoring device 4 is located.

The stay cable 2 comprises a set of traction reinforcements 10 which, inthe example considered, consist of metal strands, each covered with anindividual plastic sheath. In the running part of the stay cable, saidrunning part extending over the greatest part of its course between thedeck and the pylon, the strands 10 are gathered into a compact parallelbundle. The transverse arrangement of the strands 10 in the running partis, for example, that illustrated in FIG. 5, where there is maximumcompactness, since the strands, of circular outer shape, are in contactwith one another according to a hexagonal meshwork.

To form this compact bundle of strands, a deviating collar 11, arrangedat a distance from the anchoring device 4, is closely set around the setof strands in order to cause them to converge.

The anchoring device 4 comprises a metal block 15 illustrated in crosssection in FIG. 3. The block 15 has crossing through it parallelorifices 16 which are cylindrical towards the running part of the staycable and are frustoconical towards the opposite direction. Each orifice16 receives a stripped strand and an anchoring jaw consisting of aplurality of keys in the form of a sector of a cone frustum. Theorifices 16 have some spacing between them, so as to have room toaccommodate the anchoring jaws and to obtain a sufficiently robustblock. The transverse meshwork of these orifices is homothetic to thatof the strands in the running part of the cable. Consequently, thestrands converge from the anchoring device 4 toward the running part.

The individual sheath of the strands 10 is interrupted in a chamber 17at the rear of the anchoring block 15. The residual gaps in the blockand the chamber 17 are filled with a corrosion protection material, suchas a grease. A sealing system 18, for example of the stuffing box type,as described in European patent 0 323 285, closes the chamber 17opposite the block 15 by forming a seal around the individual sheaths ofthe strands 10. The anchoring device 4 may also comprise ducts for theindividual guidance of the strands, as described in the document WO00/75453, which widen in the direction of the running part of the cable,so as to allow an angular deviation of the individual strands.

The anchoring device 4 bears longitudinally against a tube 20 connectedto the structure of the deck 1 or of the pylon 3, in order to transmitthe tractive force in the stay cable.

The stay cable illustrated in FIG. 2 is equipped with a vibrationdamping device 21 which is located on the deck side at a distance (a fewmeters) from the anchoring device 4. This device 21 serves for dampingthe transverse vibrations of the stay cable 2 with respect to the tube20 and to the anchoring device 4, which are attributable to the dynamicload variations associated with the traffic on the bridge or with theaerodynamic forces. It is, for example, of the type described inEuropean patent 0 914 521, with an annular chamber contained between thedeviation collar 11 and a supporting tube 22 fastened to the end of thetube 20, this chamber containing a viscous material affording thedamping effect. Alternatively, the viscous damping device could bemounted on an arm extending transversely between the stay cable and thedeck 1 (see European patent 0 343 054).

The stay cable thus equipped has some capacity for allowing overalldisplacements of the strands with respect to the structure. The leverarm between the exit of the anchoring device 4 and the collar 11 givesthe damper 21 a certain transverse stroke which allows angularmovements, preferably in conjunction with the ducts for the individualguidance of the strands, said ducts being present at the exit of theanchorage. These angular movements have a limited amplitude, typicallyto approximately 25 milliradians. Greater deflections would riskdamaging the strands by imparting an excessive curvature to them at theanchoring device.

However, the angular deflections occurring in the event of an earthquakemay be much higher. In order nonetheless to give the stay cableaccording to the invention earthquake protection properties, a guidemember 30 is installed between the anchoring device 4 and the collar 11and before the strands 10 are put in place.

This guide member 30 is of cylindrical general shape. As shown in FIGS.2 and 4, it may consist of a body of cast plastic resin around a steelreinforcing tube 21. The cast plastic is advantageously a polyurethaneresin which has the advantages of being easily castable, thus making itpossible for the member 30 to be shaped with great accuracy, of havingexcellent mechanical resistance properties (hardness, stability toshearing and tensile stresses) and of having good behavior in aggressivemarine environments.

The inner surface 32 of the guide member 30 is in closely set contactaround the strands, once they are installed. The cross section of thisinner surface 32, as can be seen in FIG. 4, is adapted to the peripheralshape of the bundle of parallel strands. In the example illustrated, ahexagonal cross section circumscribes the strands assembled in the formof a hexagonal meshwork. When the strands thus assembled are of a numberequal to 1+3n.(n+1), that is to say 7, 19, 37, 61, etc., the compactbundle has a hexagonal outer profile corresponding to n completeconcentric layers around a central strand. If the number of strandsprovided for supporting the load of the stay cable is not one of thesevalues, as in the depicted example where the stay cable has 43 strands(FIG. 5), the bundle is completed by dummy strands 12 within thedeviation member 30. These dummy strands 12 may be prolonged as far asthe collar 11, beyond which they are interrupted. They are not anchoredin the device 4. In the example considered, there are 61−43=18 dummystrands 12, illustrated in black in FIG. 4.

Since the member 30 is located in an intermediate position between theanchorage 4 and the collar 11, the strands 10 have, in the region ofsaid member, a spacing corresponding to a fraction of that which theyhave in the anchoring block 15. In order to position them accurately, atthe same time ensuring good bearing contact on the guide member 30, andto prevent them from becoming disorganized in the event of abruptflexural stresses, inserts are seated within the member 30 together withthe set of strands 10, 12. These inserts may consist of individualplastic sleeves 13, into which that part of the strands 10, 12 whichpasses through the member 30 is threaded. A stop plate 35 is placed atthe back of the anchoring device 4, to prevent this device from beingdisturbed by the ends of the sleeves 13 or of the dummy strands 12.

If it is not necessary for the strands to have maximum compactness inthe running part of the stay cable, the cross section of the innersurface 32 of the guide member 30 may also be circular.

The longitudinal section of the inner surface 32 of the member 30 isillustrated in FIG. 2. It has a convex curvature which, over the lengthL of the guide member 30, allows angular deflections of thereinforcements which are markedly greater (typically at least two timesgreater) than the maximum angle of convergence of the strands 10 betweenthe anchorage 4 and the running part of the stay cable. These allowedangular deflections amount, for example, to α=100 milliradians or more,whereas the maximum angle of convergence, that is to say that of theperipheral strands, is of the order of 25 milliradians.

This take-up of pronounced angular deflections is carried out with acontrolled radius of curvature, in order to avoid excessive flexuralstresses on the strands at the exit from the anchorage. This radius ofcurvature R of the longitudinal section of the inner surface 32 of themember 30 is advantageously at least 3 meters in the rear portion of themember, where it is in closely set contact around the set of strands. Inan embodiment with strands having a diameter of 15.7 mm, the radius ofcurvature R in this rear portion will typically be 4 meters.

This radius of curvature R may be constant over the length L of themember 30. In this case, the angular defection in radians allowed by themember 30 is α≈tg α=L/R. The length L may therefore be of the order of40 cm for R=4 m and α=100 milliradians.

To reduce the overall size of the guide member 30, its inner surface 32may be formed in such a way that the radius of curvature of itslongitudinal section decreases from the rear portion, where the memberis in closely set contact around the strands 10, toward the running partof the stay cable. This is possible, without too great a risk ofdamaging the strands, since the greatest angular deflections in theevent of an earthquake tend to occur when the axial stress on the staycable is not very high: it may thus be assumed that a strand subjectedto less axial stress follows a slightly more closely set curvature. Thesmallest radius of curvature, at the front end of the member 30, is, forexample, of the order of 2.5 meters.

In a particularly advantageous embodiment, the guide member 30 ismounted in a floating manner with respect to the anchorage 4. It canthus be seen, in FIG. 2, that the member 30 has a capacity fortransverse movement with respect to the tube 20 and to the anchoringdevice 4. This avoids reducing the stroke available for the functioningof the damper 20 and therefore impairing its dynamic behavior. Thiscapacity for transverse movement of the guide member 30 is limited so asto provide a defined stroke of the damper 21.

The floating guide member 30 is, in principle, held longitudinally,since it is in closely set contact around the set of strands. To preventit from nevertheless undergoing appreciable displacements, it may beprolonged axially by means of spacers 33, 34, for example of tubularshape, which butt respectively on the damper 21 and on the stop plate 35in the event of longitudinal movements.

An earthquake gives rise to abrupt variations in moment of flexion inthe anchoring zones of the stay cables. These abrupt variations arepoorly filtered by the damper 21. This risks resulting in serious damageto the anchoring zone, especially to the tube 20, requiring majorrepairs, along with the dismantling of the anchorage and even of thestay cable. To limit this risk, there is advantageously provision forthe connection between the tube 20 and the support 22 of the damper tobe designed to break when said connection is subjected to a forceexceeding a predefined threshold.

In the example illustrated in FIG. 2, this connection is made by meansof bolts 40 which axially clamp flanges 38, 39 formed respectively atthe mutually confronting ends of the tube 20 and of the support 22. Thediameter of these bolts 40 is selected so that they break before thetransverse force reaches 4% of the axial force, thus limiting the momentof flexion transferred to the tube 20 and allowing the guide member 30to function under optimum conditions.

The possible break of these bolts 40 is relatively minor, since they areeasily replaced.

It will be understood that the exemplary embodiment which has just beendescribed does not limit the scope of the invention and that numerousvariants may be made to it. In particular, a guide member 30, asdescribed above, may be located in the region of a top anchorage, towardthe pylon. It may, on the other hand, be installed, without any devicefor damping vibrations on the stay cable.

On the other hand, the guide member 30 may belong to the means fordeviating the reinforcements, which ensure that the latter converge intoa compact bundle. It may, in particular, be substituted for the collar11 shown in FIG. 2, if the size constraints in the anchoring zone allowthis.

1. A civil engineering structure cable, comprising: a set of tractionreinforcements; two devices for anchoring the reinforcements in tworespective zones of the construction, the reinforcements being spacedapart from one another at the anchoring devices; means for deviating thereinforcements to cause the reinforcements to converge toward a runningpart of the cable into a substantially parallel bundle more compact thanat the anchoring devices; at least one guide member which is in closelyset contact around the set of reinforcements in the portion of the cablewhere the reinforcements converge toward the running part, said guidemember having an inner surface presenting a cross section is adapted toa peripheral shape of the parallel bundle and a longitudinal sectionhaving a convex curvature whereby, over the length of the guide member,said convex curvature allows angular deflections of the reinforcementsup to an angle substantially greater than a maximum angle of convergenceof the reinforcements between the anchoring device and the running partof the cable.
 2. The structure cable as claimed in claim 1, wherein theangular deflections allowed by the guide member are at least double themaximum angle of convergence of the reinforcements between the anchoringdevice and the running part of the cable.
 3. The structure cable asclaimed in claim 1, wherein the angular deflections allowed by the guidemember are of at least 100 milliradians.
 4. The structure cable asclaimed in claim 1, wherein the longitudinal section of the innersurface of the guide member has a radius of curvature of at least 3meters in the a portion where said guide member is in closely setcontact around the set of reinforcements.
 5. The structure cable asclaimed in claim 4, wherein the radius of curvature of the longitudinalsection of the inner surface of the guide member decreases from theportion where the member is in closely set contact around the set ofreinforcements toward the running part of the cable.
 6. The structurecable as claimed in claim 1, wherein the guide member is mounted with acapacity for transverse movement with respect to one of the anchoringdevices.
 7. The structure cable as claimed in claim 1, furthercomprising means for damping transverse vibrations of the bundle ofreinforcements with respect to one of the anchoring devices, and whereinthe guide member is placed on the set of reinforcements between thedamping means and said anchoring device.
 8. The structure cable asclaimed in claim 7, wherein the guide member is mounted with a limitedcapacity for transverse movement with respect to said anchoring device,so as to provide a defined stroke of the damping means.
 9. The structurecable as claimed in claim 7, wherein the anchoring device bearslongitudinally against a tube connected to the structure of a part ofthe construction and having the reinforcements extending therethrough,wherein the damping means comprise a damper arranged between the bundleof reinforcements and a support mounted at an end of said tube oppositethe anchoring device, and wherein the support is mounted at the end ofthe tube by means of a connection designed to break when subjected to aforce exceeding a predefined threshold.
 10. The structure cable asclaimed in claim 1, wherein the deviation means comprise a collarclamped around the set of reinforcements at a distance from an anchoringdevice, and wherein the guide member is placed on the set ofreinforcements between said collar and said anchoring device.
 11. Thestructure cable as claimed in claim 10, wherein inserts are seated,together with the reinforcements, in the guide member, so as to maintaina spacing between the reinforcements inside the guide member.
 12. Thestructure cable as claimed in claim 11, wherein said inserts compriseplastic sleeves placed individually around the reinforcements inside theguide member.
 13. The structure cable as claimed in claim 12, whereinthe inner surface of the guide member has a hexagonal cross section. 14.The structure cable as claimed in claim 1, wherein the guide memberbelongs to the deviation means, and contribute to causing thereinforcements to converge toward the running part of the cable.
 15. Thestructure cable as claimed in claim 1, wherein the guide membercomprises a body of cast plastic resin around a metal reinforcing tube.16. The structure cable as claimed in claim 15, wherein the plasticresin is a polyurethane resin. 17-24. (canceled)